Arsenal facing midfield crisis

Arsene Wenger has admitted Arsenal do not know how long Mesut Ozil will be sidelined with a hamstring injury and that Aaron Ramsey has struggled with his rehabilitation.

Ozil and Ramsey, as well as Jack Wilshere, will miss Sunday's north London derby against Tottenham and could leave the club battling for the FA Cup and the Premier League with an under-strength midfield.

Ozil, the German playmaker, was substituted at half-time of the 1-1 Champions League draw against Bayern Munich on Tuesday evening with a hamstring injury, while Ramsey has been out with a thigh strain since December.

"Ozil is out. I don't know for how long but it is a hamstring injury," Wenger told the club's official site. "There are scans going on."

"We have had to defer Ramsey's comeback to full training a little so he is not available. He is having difficulties in the final stages of his rehab. It looks to be short-term."

Ozil himself took to Facebook to confirm his injury. He said: "dear friends, now it's clear: during the #ucl match against #FCBayern I suffered a muscle injury in the second minute. I tried to give my best and played until the end of the first half. rest assured that I'll be back even stronger!"

There was better news for the Arsenal manager regarding Kim Kallstrom, a loan signing from Spartak Moscow who is yet to appear due to a back injury.

Kallstrom, alongside Yaya Sanogo, could be named in the squad to face Tottenham on Sunday.

Kieran Gibbs will have a fitness test on Friday before a decision is made regarding his inclusion, but Wenger is hopeful Nacho Monreal will be fit to play.